1. Field of the Invention
The present invention is generally directed toward aluminum dipping ladies and, more particularly, toward a method of controlling dipping ladle cup motion to reduce formation of aluminum oxide.
2. Description of Related Art
In an aluminum die casting process, molten aluminum is mechanically delivered from a dipwell of the furnace to the shot sleeve of the die case machine by a ladle cup. The ladle cup is a portion of a ladling unit or assembly, which includes a mechanical ladle arm and a carriage to move the ladle cup between the dipwell and the shot sleeve.
With reference to FIGS. 1a-1c, a conventional ladle cup filling process is illustrated. In this prior art method, the ladle assembly 10 includes a ladle cup 12 and a mechanical ladle arm 14. The ladle cup 12 is generally bowl shaped and includes an open rim 16, a rear edge 18 pivotally secured to the ladle arm 14, and a front edge 20 opposite the rear edge 18. During the method, the ladle cup 12 is positioned vertically adjacent the surface 22 of the molten aluminum contained within the dipwell 24 (FIG. 1a). Thereafter, the ladle cup 12 is rotated (clockwise in FIG. 1b) to a desired angular orientation representing a predetermined shot weight, which is calculated by the die cast machine controller based upon a desired shot weight entered by the machine operator. This step is referred to in the art as the xe2x80x9cshot weight angle adjustxe2x80x9d.
Thereafter, the ladle arm 14 and ladle cup 12 are lowered, while the ladle cup 12 is retained at the desired angular orientation. As the front edge 20 of the cup rim 16 drops beneath the surface 22 of the molten aluminum, the molten aluminum overflows into the ladle cup rim 16 and rushes into the ladle cup 12 with great turbulence, as indicated by the arrows in FIG. 1c. After filling of the ladle cup 12 is complete, the ladle cup is withdrawn from the dipwell 24, while maintained in the desired angular orientation, and is transported to the shot sleeve (not shown).
Unfortunately, aggressive filling of the ladle cup 12 according to the prior art method causes air to be mixed with the molten aluminum, both the molten aluminum in the ladle cup and, perhaps to a lesser extent, the molten aluminum outside of the ladle cup and remaining in the dipwell, and causes aluminum oxides to be formed. The aluminum oxides withdrawn by the ladle cup 12 will be cast with the molten aluminum in that pour or shot. The aluminum oxides remaining in the molten aluminum bath can be later picked up by the ladle cup 12 and cast in subsequent shots.
Aluminum oxide is a very hard material, especially when compared with aluminum. When cast into a part, aluminum oxides define localized hard spots that are detrimental to the tooling used in subsequent machining of the cast part. The aluminum oxides often damage or prematurely wear the tooling. Accordingly, formation of aluminum oxides and inclusion of aluminum oxides in cast parts results in machine downtime, tooling replacement costs, increased labor, and lower parts yield.
In response to this problem, aluminum die casters have attempted to slow the rate of insertion of the ladle cup, which is in the shot weight angle adjust position, into the bath of molten aluminum. Unfortunately, due to the manner in which molten aluminum overflows and tumbles as it enters the ladle cup, slowing the rate of insertion has had little effect in reducing the formation of aluminum oxides. Additional countermeasures, such as filtering of the molten aluminum, fluxing of the aluminum bath, and more frequent skimming and cleaning of the dipwell, have also been proposed. However, these additional countermeasures have proven ineffective in significantly reducing the introduction of aluminum oxides into the cast parts and, more importantly, have not significantly reduced the amount of parts sent to machining with aluminum oxide impurities.
The present invention is directed toward an improved method of filling a ladle cup with molten aluminum in which the formation of aluminum oxides is reduced or minimized.
In accordance with the present invention, the ladle cup is pivotally mounted to a ladle arm. The ladle cup and ladle arm are disposed over the bath of molten aluminum, and the ladle cup is rotated into alignment with an axis of the ladle arm. As such, a plane defined by the ladle cup rim is generally parallel to the ladle arm axis and the ladle cup opening faces generally parallel to a surface of the molten aluminum. The ladle cup is inserted into the bath of molten aluminum while maintained in alignment with the ladle arm axis, thereby allowing the molten aluminum to gently flow into and fill the ladle cup as the ladle cup is further lowered to its final position within the bath of molten aluminum. Thereafter, the ladle cup is rotated to a desired angular orientation, which corresponds to a desired shot weight or volume of molten aluminum within the ladle cup. While the ladle cup is retained in the desired angular orientation, the ladle cup is raised out of the molten aluminum.